System and method to reduce noise in a substrate

ABSTRACT

Certain embodiments of the invention may be found in, for example, a system that reduces noise in a substrate of a chip and may comprise a substrate and a first well disposed on top of the substrate. The first well may be a deep well. Notwithstanding, a second well and a third are both disposed within the first well and a first transistor may be disposed in the second well. A quiet voltage source may be connected to a body of the first transistor and a second transistor may be disposed in the third well. The first transistor may be a PMOS transistor and the second transistor may be an NMOS transistor. A noisy voltage source may be coupled to a source of the first transistor and a body of the first transistor may be resistively coupled to the second well.

CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE

This application is a continuation of U.S. application Ser. No. 10/294,880 filed on Nov. 14, 2002 now U.S. Pat. No. 6,870,228, which makes reference to, claims priority to and claims the benefit of U.S. Provisional Patent Application Ser. Nos. 60/402,095 filed on Aug. 7, 2002 and 60/402,090 filed on Aug. 9, 2002.

FIELD OF THE INVENTION

Certain embodiments of the invention relate to integrated circuit (IC) designs. More specifically, certain embodiments of the invention relate to a system for reducing noise in a substrate of an integrated circuit.

BACKGROUND OF THE INVENTION

As more and more functional blocks are added, for example, to a chip, an integrated circuit (IC) or an integrated system or device, the risk for the generation and propagation of noise between the different functional blocks or within a functional block may become quite substantial.

An exemplary conventional complementary metal oxide semiconductor (CMOS) transistor arrangement is illustrated in FIG. 1. As shown in FIG. 1, the conventional CMOS transistor arrangement 10 includes an n-channel MOS (NMOS) transistor 30 and a p-channel MOS (PMOS) transistor 40. The conventional CMOS arrangement 10 also includes a p-substrate 20 (e.g., a p⁻-substrate). The NMOS transistor 30 is disposed in the p-substrate 20. The NMOS transistor 30 includes a p⁺-body (B), an n⁺-source (S) and an n⁺-drain (D) disposed in the p-substrate 20. A voltage source V_(SS) 7 having a ground is coupled to the p⁺-body (B) and the n⁺-source (S) of NMOS transistor 30. An input line 5 is coupled to a gate (G) of the NMOS transistor 30. An output line 15 is coupled to the n⁺-drain (D) of the NMOS transistor 30. The PMOS transistor 40 includes an n-well 50 that is disposed in the p-substrate 20. The PMOS transistor 40 also includes an n⁺-body (B), a p⁺-source (S) and a p⁺-drain (D) disposed in the n-well 50. A voltage source V_(DD) 17 is coupled to the p⁺-source (S) and the n⁺-body (B) of PMOS transistor 50. The input line 5 is also coupled to a gate of the PMOS transistor 40. The output line 15 is also coupled to the p⁺-drain (D) of the PMOS transistor 40.

During normal operation of the conventional CMOS transistor arrangement 10, the voltage sources V_(SS) 7, V_(DD) 17 may be noisy. For example, the noise may be caused by other circuitry found on or coupled to the chip that may directly or indirectly affect the voltage sources V_(SS) 7, V_(DD) 17. High swing or high power devices such as, data drivers in a wire line communication system or transmitters in wireless communications systems, may be sources of noise. The noise may also be caused, for example, by the driving of active circuits. In one example, the voltage sources may be coupled to active circuitry (e.g., active portions of an inverter circuit) which may cause transient currents to flow during signal transitions from a high level to a low level or from a low level to a high level. In another example, noise may be caused by transitions in a signal propagated or generated by the chip.

In the NMOS transistor 30, if the voltage source V_(SS) 7 is noisy, then the noise may propagate to the p-substrate 20 via, for example, at least through the resistive coupling 9 between the p⁺-body (B) and the p-substrate 20. In the PMOS transistor 40, if the voltage source V_(DD) 17 is noisy, then the noise may propagate to the n-well 50 via the n⁺-body (B) of the PMOS transistor 40 via a resistive coupling 19. The noise in the n-well 50 may propagate to the p-substrate 20 via, for example, at least the capacitive coupling 29 between the n-well 50 and the p-substrate 20. If the noise is able to propagate to the p-substrate 20, then noise may propagate to or otherwise affect other circuits on or off the chip that may be coupled to the p-substrate 20.

FIG. 1A shows another conventional CMOS arrangement 10, which is similar to the conventional CMOS arrangement 10 shown in FIG. 1, except that a quieter voltage source V_(SS) 3 is coupled to the p⁺-body (B) of the NMOS transistor 30 and a noisy voltage source V_(SS) 7 is coupled to the n⁺-source (S) of the NMOS transistor 30. Thus, less noise is resistively coupled from the p⁺-body (B) to the p-substrate 20. To a lesser extent, noise may be capacitively coupled between the n⁺-source and the p-substrate 20. Noise may be coupled from the PMOS transistor 40 to the p-substrate 20 as described above with respect to the conventional CMOS arrangement 10 as shown in FIG. 1. In the CMOS arrangement of FIG. 1A, noise may substantially propagate to the p-substrate 20. Accordingly, there is a need to mitigate noise in the substrate of a chip.

Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.

BRIEF SUMMARY OF THE INVENTION

Certain embodiments of the invention may be found in, for example, a system that reduces noise in a substrate of a chip. Aspects of the system may comprise a substrate and a first well disposed on top of the substrate. The first well may be a deep well. A second well and a third are both disposed within the first well and a first transistor may be disposed in the second well. A quiet voltage source may be connected to a body of the first transistor and a second transistor may be disposed in the third well. The first transistor may be a PMOS transistor and the second transistor may be an NMOS transistor. A noisy voltage source may be coupled to a source of the first transistor and a body of the first transistor may be resistively coupled to the second well.

The system may further comprise a noisy voltage source, and a body and a source of the second transistor may both be coupled to the noisy voltage source. The body of the second transistor may be capacitively coupled to the substrate. The substrate and the third well may be doped with a first dopant and the first and the second well may be doped with a second dopant.

These and other advantages, aspects and novel features of the present invention, as well as details of an illustrated embodiment thereof, will be more fully understood from the following description and drawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIGS. 1 and 1A shows embodiments of conventional complementary metal oxide semiconductor (CMOS) transistor arrangements.

FIG. 2 shows an embodiment of a CMOS transistor arrangement according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 shows an embodiment of a complementary metal oxide semiconductor (CMOS) transistor arrangement 60 in accordance with the present invention. The CMOS transistor arrangement 60 may include a p-substrate 70, a deep n-well 80, an n-channel MOS (NMOS) transistor 90 and a p-channel MOS (PMOS) transistor 100. The NMOS transistor 90 may include, for example, a p⁺-body (B), an n⁺-source (S) and an n⁺-drain (D) which may be disposed in a p-well 110. The p-well 110 may be an isolated p-well since, for example, it may be disposed between two n-wells 120 and the deep n-well 80. A voltage source V_(SS) 170 having an electrical ground, may be coupled to the p⁺-body (B) and the n⁺-source (S) of the NMOS transistor 90. An input signal line 150 may be coupled to a gate of the NMOS transistor 90. An output signal line 160 may be coupled to the n⁺-drain of the NMOS transistor 90.

The PMOS transistor 100 may include, for example, an n⁺-body (B), a p⁺-source (S) and a p⁺-drain (D), which may be disposed in an n-well 120. A first voltage source V_(DD) 130 may be coupled to the p⁺-source (S) and a second voltage source V_(DD) 140 may be coupled to the n⁺-body (B) of the PMOS transistor 100. In one embodiment, the second voltage source V_(DD) 140 is less noisy than the first voltage source V_(DD) 130. In this regard, V_(DD) 140 may be a quieter voltage source in comparison to the voltage source V_(DD) 130. The input signal line 150 may be coupled to a gate of the PMOS transistor 100. The output signal line 160 may be coupled to the p⁺-drain (D) of the PMOS transistor 100.

The voltage source V_(DD) 130 and the quieter voltage source V_(DD) 140 may be different voltage sources. The quieter voltage source V_(DD) 140 may be a dedicated voltage source that is not coupled to some sources of noise. For example, it can be an active component of a transistor. The quieter voltage source V_(DD) 140 may be dedicated, for example, to a guard bar for well taps or substrate taps. Alternatively, the voltage source V_(DD) 130 and the quieter voltage source V_(DD) 140 may be coupled to the same voltage source. However, the quieter voltage source V_(DD) 140 may be isolated or separated from the voltage source V_(DD) 130 so that less noise may be carried by the quieter voltage source V_(DD) 140.

In operation, the voltage source V_(SS) 170 and the voltage source V_(DD) 130 may be noisy due to a number of factors, some of which are described herein. For example, the noise may be caused by other circuitry found on or coupled to the chip that may directly or indirectly affect the voltage sources V_(SS) 170, V_(DD) 130. High swing or high power devices such as, data drivers in a wire line communication system or transmitters in wireless communications systems, may be sources of noise. The noise may also be caused, for example, by the driving of active circuits. In one example, the voltage sources may be coupled to active circuitry (e.g., active portions of an inverter circuit) which may cause transient currents to flow during signal transitions from a high level to a low level or from a low level to a high level. In another example, noise may be caused by transitions in a signal propagated or generated by the chip and/or any associated circuitry.

In accordance with the inventive CMOS transistor arrangement 60, one source of noise is that the voltage sources V_(SS) 170, V_(DD) 130 may be coupled to the sources of the NMOS transistor 90 and the PMOS transistor 100. Thus, for example, when the circuit is in a transitional state such as during a signal transition from a high level to a low level or from a low level to a high level, a transient current may flow between the voltage sources V_(SS) 170 and V_(DD) 130. Notably, if other devices (e.g., other CMOS transistor arrangements) are sharing the voltage sources V_(SS) 170, V_(DD) 130, then the noise generated by the transient current flows may be substantial.

The noise in the voltage source V_(SS) 170 may flow into the body (B) and the source (S) of the NMOS transistor 90. The body (B) of the NMOS transistor 90 may be resistively coupled 180 to the p-well 110 and the source (S) of the NMOS transistor 90 may be capacitively coupled 190 to the p-well 110. The resistive coupling 180 may be much more substantial than the capacitive coupling 190. Accordingly, most of the noise in the p-well 110 may be associated with the p⁺-body of the NMOS transistor 90. For the noise in the p-well 110 to reach the p-substrate 70, the noise may need to pass through two capacitive couplings: a capacitive coupling 200 between the p-well 110 and the deep n-well 80 and a capacitive coupling 210 between the deep n-well 80 and the p-substrate 70. Importantly, the capacitive coupling is generally fairly weak, but the capacitive coupling is even weaker when the couplings are placed in series. Thus, in this embodiment of the present invention, the resistive couplings 180, 200 and 210 between the p⁺-body (B) of the NMOS transistor 90 through to the p-substrate 70 may be replaced with a much weaker capacitive coupling.

The noise in the voltage source V_(DD) 130 may flow into the p⁺-source (S) of the PMOS transistor 100. In this embodiment, the present invention may employ a quieter voltage source V_(DD) 140 which may be coupled to the n⁺-body (B) of the PMOS transistor 100. The p⁺-source (S) of the PMOS transistor 100 may be capacitively coupled 220 to the n-well 120 and the n⁺-body (B) of the PMOS transistor 100 may be resistively coupled 230 to the n-well 120. Since the resistive coupling 230 may be more substantial than the capacitive coupling, the noise in the n-well 120 may be mostly from the quieter voltage source V_(DD) 140. Advantageously, the noise in the n-well 120 may be substantially reduced by connecting the quieter voltage source V_(DD) 140 to the n⁺-body (B) of the PMOS transistor 100. The n-well 120 and the deep n-well 80 may be resistively coupled 240. Notably, the deep n-well 80 may provide a substantial amount of resistance to the noise, thereby further reducing any noise propagating through PMOS resistor 100 and reaching substrate 70. The deep n-well 80 and the p-substrate 70 may be capacitively coupled, which may offer the noise only a weak coupling.

Although illustrated in use with a CMOS transistor arrangement, the present invention need not be so limited. The present invention may also be applicable for use with other types of transistors or other types of transistor arrangements. Notably, in a an embodiment of the invention, the quiet V_(dd) may be used to replace a conventional V_(ss) without an area penalty. In this regard, the area used by the V_(dd) may replace the area used by the V_(ss), in for example, a block or standard resistor/transistor logic (RTL) arrangement. The present invention may also be applicable for use with other electrical, magnetic or electromagnetic components or circuits. Furthermore, although one or more of the embodiments described above may employ semiconductor materials (e.g., semiconductor material, compound semiconductor material, etc.), the present invention may also contemplate using other materials (e.g., ceramics, metals, alloys, superconductors, etc.) or combinations thereof. In addition, the present invention may also contemplate using different dopant types, dopant schemes or dopant concentrations other than or in addition to the above-described dopant types, dopant schemes or dopant concentrations.

While the present invention has been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the present invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present invention without departing from its scope. Therefore, it is intended that the present invention not be limited to the particular embodiment disclosed, but that the present invention will include all embodiments falling within the scope of the appended claims. 

1. A system for reducing noise in a chip, the system comprising: a substrate; a first well disposed on top of said substrate; a second well and a third well that are both disposed within said first well; a first transistor disposed in said second well; a positive potential of a quiet voltage source connected to a body of said first transistor; and a second transistor disposed in said third well.
 2. The system according to claim 1, wherein said first transistor is a PMOS transistor.
 3. The system according to claim 1, wherein said second transistor is an NMOS transistor.
 4. The system according to claim 1, further comprising a noisy voltage source coupled to a source of said first transistor.
 5. The system according to claim 1, wherein a body of said first transistor is resistively coupled to said second well.
 6. The system according to claim 1, further comprising a noisy voltage source, wherein a body and a source of said second transistor are both coupled to said noisy voltage source.
 7. The system according to claim 1, wherein a body of said second transistor is capacitively coupled to said substrate.
 8. The system according to claim 1, wherein said first well is a deep well.
 9. The system according to claim 1, wherein said substrate is doped with a first dopant.
 10. The system according to claim 1, wherein said first well is doped with a second dopant.
 11. The system according to claim 1, wherein said second well is doped with a second dopant.
 12. The system according to claim 1, wherein said third well is doped with a first dopant. 